A pipe is often used for conveying fluid, and a valve is provided between the pipes for switching control of the pipeline. In order to achieve the purpose of fast switching, there has been developed a plug valve. The plug valve comprises a valve seat. The valve seat has a passage therein. The passage is provided with a plug. The plug is radially formed with a through hole corresponding to the passage. The plug is further connected with an operation handle. The user can operate the operation handle to rotate the plug relative to the valve seat. When the through hole corresponds to the passage, the fluid will pass through the plug valve. When the through hole and the passage are staggered, the fluid is blocked by the plug and cannot pass through the plug valve.
In addition, in order to achieve the purpose of adjusting the flow of the pipeline, the industry has developed a fine adjustment valve. The fine adjustment valve comprises a valve seat. The valve seat has a passage therein. The passage is radially communicated with a screw hole. A screw rod is threadedly provided in the screw hole. The user can adjust the depth of the screw rod inserted into the passage to change the sectional area of the passage so as to adjust the flow.
However, although the foregoing plug valve can control the passage to be fully opened or closed in a quick manner, the flow is adjusted only by adjusting the relative angle between the through hole and the passage, i.e., changing the overlapping area of the through hole and the passage. Because the relative angle between the through hole and the passage cannot be fixed, it is difficult to fix the flow after each switching. This way cannot accurately adjust the flow of the passage. Although the foregoing fine adjustment valve can accurately adjust the flow of the passage, when it is necessary to control the passage to be fully opened or closed, the user needs to constantly rotate the operation member for the screw rod to leave or block the passage. This operation is very inconvenient. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.